When there is a kidney dysfunction, water and waste products that have to be discharged out of body accumulate in blood and imbalance of electrolytes in the body occurs. Most commonly performed to improve such a kidney failure symptom, is hemodialysis which is to circulate blood out of body and rid the blood of the accumulated uremic toxin and excess water by a semi-permeable dialysis membrane. Hemodialysis is a method of seeking an electrolyte balance and ridding the body fluid of uremic toxin and excess water, taking advantages of diffusion applied due to the concentration difference and filtration applied due to the pressure difference between blood and dialysate, while circulating blood through a side of the semi-permeable membrane and dialysate through the other side thereof.
A hemodialyzer having a structure where semi-permeable membrane is disposed in a single container is used such that mass transfer between blood and dialysate easily occurs. Most commonly used of the hemodialyzer is the hollow-fiber membrane type that is a cylinder-shape container charged with a semi-permeable membranes and port-processed at opposite ends thereof by use of a synthetic resin like polyurethane.
Blood and dialysate each decrease their hydraulic pressure while passing through a hemodialyzer. Since blood and dialysate flow in opposite directions inside the hemodialyzer, filtration occurs at the proximal part of the hemodialyzer such that water in the blood moves toward dialysate compartment because blood pressure is higher than dialysate pressure, while backfiltration occurs at the distal part such that water in the dialysate moves toward blood domain for the same reason.
When water in the blood moves toward the dialysate compartment, wastes in blood are also eliminated, which is referred to as a convective mass transfer. It is known that uremic toxins of medium molecular size are efficiently removed by the convective mass transfer and thus dialysis efficiency and prognosis on patients have greatly improved. However, there is a big hurdle in the effort to improve dialysis efficiency by the convective mass transfer, because hemodialyzers in typical hemodialysis apparatuses are limited in size and blood flow rate is restrictively allowed to be increased in consideration of the weight and blood vessel condition of a patient.